Paper-based products, such as paper towels, facial tissues and other similar products, are designed to include several important properties. For example, the products should have good bulk, a soft feel and should be highly absorbent. The product should also have good strength, even when wet, and should resist tearing. Unfortunately, it is very difficult to produce a high strength paper product that is also soft. Usually, when steps are taken to increase one property of the product, other characteristics of the product are adversely affected.
For instance, strength is typically increased by the addition of strength agents to the product. Although the strength of the paper product is increased by such strength agents, the resulting paper product is generally not soft. In particular, cellulosic fibers contain a number of functional groups (e.g., hydroxyl groups, carboxyl groups, etc.) that form hydrogen bonds with adjacent cellulosic fibers. These hydrogen bonds restrict the movement of adjacent cellulosic fibers and thus result in a product that feels relatively stiff. Consequently, paper-based products are conventionally softened using mechanical techniques (e.g., creping) or with chemical debonders. These softening techniques disrupt the hydrogen bonds formed between adjacent cellulosic fibers break, thereby resulting in a web that has improved softness.
Unfortunately, however, conventional softening techniques sometimes result in problems. For example, due to the extensive mechanical forces required during creping, it is often difficult to control the extent of softening and strength reduction. Moreover, the properties of the product may vary for a new creping blade and a used creping blade. In addition, chemical debonders require the incorporation of chemical compounds during paper formation, which may be time consuming and costly in many applications. As such, a need currently exists for an improved method of softening a paper-based product.
In accordance with one embodiment of the present invention, a method of softening a cellulosic fibrous material is disclosed that comprises exposing the material to ionizing radiation at a dosage of from about 0.1 megarads to about 10 megarads, and in some embodiments, from about 1 megarad to about 5 megarads. The ionizing radiation has a wavelength of from about 10xe2x88x9214 meters to about 10xe2x88x925 meters, and in some embodiments, from about 10xe2x88x9213 meters to about 10xe2x88x929 meters.
In accordance with another embodiment of the present invention, a method is disclosed for softening a paper web that is formed from a papermaking furnish that contains cellulosic fibers and dried to a solids consistency of greater than about 95%. The method comprises exposing the dried paper web to electron beam radiation at a dosage of from about 0.1 to about 10 megarads. In one embodiment, the paper web is dried with a through-dryer. Further, if desired, the paper web may be formed without creping.
Other features and aspects of the present invention are discussed in greater detail below.